Geographic Range

Blue chromis are found primarily in the western portion of the Atlantic Ocean, including the Gulf of Mexico and the Caribbean Sea, and extending to Bermuda and the Lesser Antilles (10-32°N). (Allen, 1991; Froese and Luna, 2012; Mertz, 2003)

Habitat

Blue chromis are found in lagoons and reef communities at depths of 3 to 60 meters; they are found most commonly at depths of 10-20 meters, where food and shelter are most abundant. They prefer water temperatures of 21 to 27°C, the same parameters required for coral survival; healthy coral is of vital importance to this species, as reefs provide a location for feeding, breeding, and protection from predators. Males maintain small territories, typically comprised of a flat nesting area and an overhang or crevice with a small (approximately 7 cm in diameter) opening. They are also known to hide in fields of staghorn coral (Acropora cervicornis). Juveniles tend to school above and hide beneath or within a shelter-providing home structure, generally a coral head. They prefer yellow finger coral (Madracis mirabilis), Lamarck's sheet coral (Agaricia lamarcki) and smooth flower coral (Eusmilia fastigiata). ("Chromis cyanea", 2012; De Boer, 1978; De Boer, 1980; De Boer, 1981; Hurley and Hartline, 1974; Michael, 2008)

Physical Description

Adults have an average total body length of about 13 cm (15 cm maximum). The body is compressed and oval in shape. These fish have a small, terminal mouth, continuous dorsal fin (12 dorsal fin spines and 12 dorsal soft rays) and deeply forked tail (2 anal spines and 12 anal soft rays). They are a bright, iridescent blue in color, with a black dorsal stripe and black margins on the dorsal fin, upper and lower lobes of the caudal fins, and front of the anal fin. They can be distinguished from similar species, such as juvenile black snapper (Apsilus dentatus) and blue hamlet (Hypoplectrus gemma), by their dark eyes and the continuation of their black dorsal stripe to the upper and lower margins of the tail. Males may exhibit any one of five color morphs, including dark grey-blue and light blue shades, with accompanying variations in dorsal stripe thickness. Sexual dimorphism occurs only during spawning, when females can be identified from light blue or dark-colored displaying males by their swollen bellies and protruding white genital papilla. (Allen, 1991; Bunkley-Williams and Williams, 2000; De Boer, 1980; Froese and Luna, 2012; Humann and DeLoach, 2002; Lieske and Myers, 2002; Mertz, 2003)

Development

Blue chromis begin life as soft, translucent, demersal eggs, adhered to the substrate. The eggs are tended to by the male for 2 to 3 days before hatching into fast-swimming larvae. The larval stage lasts 17-47 days. These larvae stay within the cover of the reef surrounding the nest until they reach about 1 cm in length; they then join other juveniles in aggregations above the reef to feed on zooplankton. Juveniles, which have a more compact body shape than adults, school together until reaching 5-6 cm in length. After this they become sexually mature, at which point males begin to defend territories and maintain nests of their own. (Breder and Rosen, 1966; De Boer, 1978; John and Hanel, 2008; Michael, 2008)

Reproduction

Blue chromis are promiscuous, with multiple females visiting and laying eggs at many nests and males mating with multiple females. Male reproductive success may be determined by the condition and location of the nest, as well as the presence of eggs already in the nest. (De Boer, 1980; De Boer, 1981; Michael, 2008)

To solicit females, males may perform a maneuver called a signal jump in which they rapidly propel themselves up vertically and then loop back to the starting position. They may also perform "dipping," where they swim in a zig-zag fashion above their territories. Males will present to females, swimming laterally and rotating 180 degrees for inspection. If a female indicates receptivity and the display is not interrupted, the male will lead her to his nest using an exaggerated side to side swimming motion. She will "nip" at the floor of the nest, and the male will respond by quivering his fins and skimming over the subtrate. He may nudge the female's genital papilla with his snout to encourage oviposition (known as butting). Once eggs are laid, a male will release milt (seminal fluid); it is not known precisely when the male releases milt, but it is hypothesized that it is dispersed by tail wagging. A male may begin to solicit another mate while one female is laying eggs in his nest. Spawning ends when the female is spent; she will either leave the nest immediately or be chased out. Other males may interfere in breeding, since displays take place up to 1 meter above a nest (outside territorial borders). Males may also sneak into nests while their owner is occupied in a display, preemptively fertilizing deposited eggs. (De Boer, 1980; De Boer, 1981; Michael, 2008)

Female blue chromis have synchronized ovarian cycles and spawning occurs once a month, generally during the full moon. The spawning period lasts 3 to 7 days, during which time females both actively seek out males and are solicited. In most Chromis species, each clutch produced by a single female contains around 40,000 eggs. Eggs hatch into independent larvae within 2 to 3 days of spawning and are cared for by males. Juveniles reach sexual maturity within 47 days. Males maintain territories throughout the year, though increases in the number of larvae observed during the months of June and October indicate that reproduction may have a seasonal component. (De Boer, 1980; De Boer, 1981; Michael, 2008)

Blue chromis spawn multiple times during monthly 3-7 day spans, often during the full moon.

Breeding season

Reproduction peaks in June and October.

Average number of offspring

40,000

Range time to hatching

2 to 3 days

Range time to independence

17 to 47 days

Range age at sexual or reproductive maturity (female)

17 to 47 days

Range age at sexual or reproductive maturity (male)

17 to 47 days

Male blue chromis assume responsibility for all parental care, from nest preparation to caring for eggs. Small areas of sand, coral, or algae-covered rock are cleared by "nipping" (removing material orally) or generation of water currents by tail fanning. Males care for eggs and larvae by chasing away similarly-sized predators, nipping away debris, and moving water over the eggs. (De Boer, 1980; De Boer, 1981)

Lifespan/Longevity

Lifespan is estimated to exceed 5 years in captivity. Little is known about lifespan in the wild, although density-driven early mortality is thought to occur. (Hixon and Carr, 1997; Michael, 2008)

Range lifespanStatus: captivity

5 (low) years

Typical lifespanStatus: captivity

5 (low) years

Behavior

Blue chromis are diurnal, feeding during the day and hiding at night. Juveniles often school and feed together in loose aggregations. Adult males are solitary and highly territorial. They perform distinct behavioral displays to maintain their territories, including chasing, pushing, butting, or ramming intruders out of nests, and swimming in parallel with neighbors to reinforce boundaries. These tactics may be accompanied by color changes, with brighter colors signifying aggression or dominance. If kept in captivity, dominance hierarchies develop; in small schools (less than six fish), individuals on the bottom of the social hierarchy may actually be harassed to death. (De Boer, 1981; Hixon and Carr, 1997; Hurley and Hartline, 1974)

Home Range

Males defend territories that vary in size from 3 m^2 up to 20 m^2, extending upward from the substrate to about 1 m. Territory size is related to population density, with males in low density areas maintaining larger territories. Females swim and feed freely between and above these territories. (De Boer, 1978; De Boer, 1981)

Communication and Perception

Blue chromis communicate mainly through visual channels. Interactions between competing males, residents and intruders, and potential mates are all marked by variations in swimming patterns and/or physical contact. Specific color changes often accompany behavioral patterns, providing the audience with additional visual clues and communicating intent. Blue chromis also use olfaction and mechanoreception (lateral line) to detect water movement and vibration, and can also hear using their well-developed inner ears. (Bond, 1996; De Boer, 1980; De Boer, 1981; Michael, 2008)

Food Habits

Blue chromis feed mainly on plankton suspended in the water column. When feeding, they remain stationary in the water column and rely on the current to bring food particles to them. Feeding is accomplished by rapid extension of the jaw, which causes prey to be sucked into the buccal cavity, due to the negative pressure generated. Feeding is frequently interrupted when blue chromis dart for cover from a perceived threat. The threat of predation increases under conditions of low prey density, when these fish must distance themselves from protective structure in order to feed. Examination of the stomach contents of blue chromis revealed that their diet is composed of about 52% copepods and 34% tunicates by volume, with the remainder comprised of shrimp larvae, siphonophores, fish eggs, and ostracods. Juveniles may also eat planktonic algae. (De Boer, 1978; Hixon and Carr, 1997; Hurley and Hartline, 1974; Randall, 1967)

Predation

As a moderately small reef fish, blue chromis are a food source for a variety of larger fish species. Predators can be resident or transient piscivores. To avoid predation, blue chromis hide under or within shelter and may also adopt a darker color morph when closer to the substrate, in order to camouflage their bodies. (De Boer, 1980; Hixon and Carr, 1997; Hurley and Hartline, 1974; Randall, 1967)

Ecosystem Roles

Blue chromis share the reef habitat with many other species of planktivorous fish and are preyed upon by larger species of fishes. Juvenile black snapper (Apsilus dentatus), which feed alongside blue chromis, mimic them in order to attack unsuspecting crustaceans. The territorial nature of these fish may often reduce the number of hiding places for other similarly-sized non-territorial fish, such as brown chromis (Chromis multilineata), increasing predation rates on these species. There is no data currently available regarding parasites of blue chromis. (Michael, 2008)

Economic Importance for Humans: Positive

Blue chromis are hardy inhabitants of saltwater aquariums and are common in the pet trade. (Michael, 2008)

Economic Importance for Humans: Negative

Conservation Status

Blue chromis are abundant throughout their geographic range, and are listed as a species of least concern by the International Union for the Conservation of Nature and Natural Resources. (Humann and DeLoach, 2002)

Glossary

the body of water between Africa, Europe, the southern ocean (above 60 degrees south latitude), and the western hemisphere. It is the second largest ocean in the world after the Pacific Ocean.

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

Neotropical

living in the southern part of the New World. In other words, Central and South America.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

carnivore

an animal that mainly eats meat

chemical

uses smells or other chemicals to communicate

coastal

the nearshore aquatic habitats near a coast, or shoreline.

cryptic

having markings, coloration, shapes, or other features that cause an animal to be camouflaged in its natural environment; being difficult to see or otherwise detect.

diurnal

active during the day, 2. lasting for one day.

dominance hierarchies

ranking system or pecking order among members of a long-term social group, where dominance status affects access to resources or mates

ectothermic

animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

external fertilization

fertilization takes place outside the female's body

fertilization

union of egg and spermatozoan

heterothermic

having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.

indeterminate growth

Animals with indeterminate growth continue to grow throughout their lives.

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

male parental care

parental care is carried out by males

motile

having the capacity to move from one place to another.

natatorial

specialized for swimming

native range

the area in which the animal is naturally found, the region in which it is endemic.

oceanic islands

islands that are not part of continental shelf areas, they are not, and have never been, connected to a continental land mass, most typically these are volcanic islands.

oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

pet trade

the business of buying and selling animals for people to keep in their homes as pets.

the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.

reef

structure produced by the calcium carbonate skeletons of coral polyps (Class Anthozoa). Coral reefs are found in warm, shallow oceans with low nutrient availability. They form the basis for rich communities of other invertebrates, plants, fish, and protists. The polyps live only on the reef surface. Because they depend on symbiotic photosynthetic algae, zooxanthellae, they cannot live where light does not penetrate.

saltwater or marine

mainly lives in oceans, seas, or other bodies of salt water.

sedentary

remains in the same area

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

solitary

lives alone

tactile

uses touch to communicate

territorial

defends an area within the home range, occupied by a single animals or group of animals of the same species and held through overt defense, display, or advertisement

tropical

the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.

vibrations

movements of a hard surface that are produced by animals as signals to others

visual

uses sight to communicate

year-round breeding

breeding takes place throughout the year

zooplankton

animal constituent of plankton; mainly small crustaceans and fish larvae. (Compare to phytoplankton.)

Disclaimer:
The Animal Diversity Web is an educational resource written largely by and for college students. ADW doesn't cover all species in the world, nor does it include all the latest scientific information about organisms we describe. Though we edit our accounts for accuracy, we cannot guarantee all information in those accounts. While ADW staff and contributors provide references to books and websites that we believe are reputable, we cannot necessarily endorse the contents of references beyond our control.

This material is based upon work supported by the
National Science Foundation
Grants DRL 0089283, DRL 0628151, DUE 0633095, DRL 0918590, and DUE 1122742. Additional support has come from the Marisla Foundation, UM College of Literature, Science, and the Arts, Museum of Zoology, and Information and Technology Services.